This invention relates to collimated aiming devices and more particularly to collimated beam combining gun sights, also known as reflex gun sights.
Reflex sights have been known for a number of years. Their design generally employs the reflection of a reticle from a semi-transparent mirror surface through which mirror the target is also viewed. A collimator is employed to cause a reticle image to appear at or near infinity, parallax free, and in focus with the target. The collimator may be a refracting lens in the system or the semi-transparent mirror may be concave instead of flat so that it collimates the reticle image as it reflects it.
The semi-transparent mirrors used in reflex sights transmit a percentage of the target light and reflect a percentage of the reticle light, the sum of which for a given frequency is not over 100%.
If a semi-transparent dichroic mirror is chosen which is not color selective and which has a sufficiently high reflection character to permit seeing the reticle against the sky, then the mirror does not transmit sufficient target light to permit seeing dimly lighted targets even though the mirror employed may be a modern 95 or 98% efficiency dichroic mirror. Conversely, if a mirror is chosen for somewhat darker targets, that mirror will not permit seeing the reticle against bright targets.
To overcome this problem, several aiming devices have been designed which attempted to make the image discernable not by brightness compared to the target brightness, but by making the image appear in a specific color which color was made brighter than the same color in the target view by employing an electric powered light source. A filter and/or a narrow band reflector mirror was employed to give the specific color to the image and the electric powered cathode ray tube provided the needed brightness, of that frequency or color to make the image sufficiently bright to be discernable, Nobles U.S. Pat. No. 2,853,974 and Noxon U.S. Pat. No. 3,230,819. Such a system is, of course, usable in a motor powered vehicle where an electric power source is available to get an intense reticle light, but is not practical for a portable shoulder arm carried by a foot soldier or a hunter.
One sight acquired the needed special brightness of the specific reticle color by employing a fluorescent material which absorbed rays from a different portion of the spectrum, such as ultra-violet and near ultra-violet, and emitted a narrow band of visible light in a lower frequency, Mauer U.S. Pat. No. 2,780,130 and the aforementioned Rickert U.S. Pat. No. 3,523,710. Such a fluorescent system provided the needed brightness of the chosen reticle frequency of color. A mirror designed to efficiently reflect this fluorescent frequency was employed, but again the mirror did not make the reticle appear a certain color it merely reflected a certain colored reticle.
Such a gun sight is presently sold on the market and works for a hunter out in the open where the sky light provides the needed ultra-violet or near ultra-violet light to operate the fluorescent material.
For a foot soldier in combat, however, where he many times shoots at his enemy from a hidden position such as hidden in the cover of trees, brush, a building or a cavelike structure, it has been found that none of the presently available fluorescent materials will operate and emit their fluorescent light when the light striking them is light reflected from the countryside. They require ultra-violet or near ultra-violet light from the open sky. Fluorescent illuminated sights have therefore been found impractical for the combat soldier.
Another sight was developed which employed a semi-transparent mirror which mirror reflected a narrow portion only of the color spectrum such as yellow (0.589 microns) or such as a farther down scale yellow orange frequency. The reticle was provided with this specific frequency by employing overhead skylight, down range skylight, and target light directed by a prism to a reticle having white reticle lines or marks, Davis U.S. Pat. No. 2,633,051.
When this sight was aimed at a target of the right brightness and also aligned to the proper reticle illuminating light sources, the reticle appeared sufficiently bright to be usable. However, when this sight was aimed at too bright a target or when the reticle light sources were not properly located, or when the sight was aimed from a cavelike structure which shaded the skylight, the reticle was then insufficiently bright to be practical.
The foregoing was given to more clearly present the problem and to more clearly define the invention.